Delicious for bookmarking and sharing bookmarks. Delicious was one of the earliest entries into the social bookmarking market. Delicious is still functional, but there are some alternatives that are worth exploring too.
Padlet Mini is the latest tool that I've tried for social bookmarking. Padlet Mini is a Chrome extension that you can use to bookmark websites. When you click the Padlet Mini extension in your browser you will be presented with the option to save to one of your existing walls (if you already have a Padlet account) or create a new Padlet wall. Padlet Mini is ideal for having students share links to interesting pages, pictures, and videos that they find about a topic that they are studying in class.
Diigo is a great option for bookmarking websites and sharing them with a group. You can use any of the many Diigo browser add-ons or mobile apps to bookmark websites. The Diigo bookmarking tools allow you to clip portions of a webpage, highlight portions of the page, and add notes to it while you bookmark. Adding those notes is helpful in letting your collaborators know why you saved a link. Diigo allows you to create public and private groups in which you share bookmarks. Creating a Diigo group is a good way for students to collaborate on a research task. Another benefit of Diigo is the option to publish a list of bookmarks to a blog. See the video that Vicki Davis made to learn how to do that.
Annotary is a social bookmarking service that is similar to Diigo. By using Annotary in Chrome I can bookmark sites, highlight portions of pages, and annotate pages with sticky notes. Just like any good online bookmarking service, Annotary allows you to share bookmarks and search other peoples' shared bookmarks.
This list wouldn't be complete without mentioning Pinterest. If your school allows it and your students are old enough to have accounts, you could use Pinterest to bookmark your web findings. A better option than Pinterest for schools is eduClipper. eduClipper is a great place for teachers and students to collaborate on the creation of visual bookmark boards. Students do not need to have email addresses to use eduClipper and you can manage how your students share on eduClipper boards. Click here for three video tutorials on using eduClipper.
Clipix will remind you of Pinterest or eduClipper in that you can "clip" images, videos, and links to save on digital clipboards. Clipix also supports uploading files from your computer to your Clipix clipboards. Each of the clipboards that you create in your Clipix account can be kept private or made public. There is also a privately shared option that can be used for collaborating on clipboard creation. Clipix offers Android and iOS apps that will synchronize with your online Clipix account.
Disclosure: I am an advisor to eduClipper.